Many configurable devices such as integrated circuits or other semiconductor devices provide multiple configuration options that may be set by users. Configurable devices with such configuration options allow semiconductor suppliers to produce programmable devices of a given design to be used in multiple applications in lieu of producing devices of a specific design customized for each application. Further, this configuration provides greater design flexibility when using the configurable devices.
A programmable device may have one or more parameters such as operating parameters that may each be configured to a selected setting. Configuration terminals such as pins or bumps may be utilized to configure the parameters of the programmable device. As illustrated in FIG. 1, a prior art technique for configuring parameters of a programmable device uses one configuration terminal for each parameter. Each configuration terminal is connected to a configuration resistor that is external to the programmable device. A resistor value of each configuration resistor is used to select the desired setting for a corresponding parameter. FIG. 2 illustrates a prior art mechanism used to determine the resistor values of the configuration resistors to determine the desired setting for each parameter. A regulated current source may be connected to one of the configuration terminals. Since the current from that configuration terminal to ground is known, the resistor value of the configuration resistor connected to that configuration terminal can be determined by measuring the voltage at the configuration terminal and applying Ohm's law. Similarly, by connecting the current source to the other configuration terminal, the resistor value of the other configuration resistor may be determined. There are many examples of parameters that may be configured. For example, as shown in an example configuration table 1 below, the parameters may include two operational parameters—a shutdown temperature for thermal protection and an operating frequency.
TABLE 1TerminalParameterSettingResistor1Shutdown Temperature50° C. 50K Ohms(Thermal Protection)60° C. 75K Ohms70° C.100K Ohms2Operating Frequency100 MHz 50K Ohms150 MHz 75K Ohms200 MHz100K Ohms
The desired setting for a parameter may be selected by connecting a resistor with a resistor value associated with the desired setting to the configuration terminal dedicated to that parameter. FIG. 2 illustrates an example with two configuration terminals, but this mechanism may be used with more configuration terminals and configuration resistors.
Although this technique is simple and reliable, it requires a dedicated configuration terminal for each parameter. This may increases the cost of programmable devices, and may also increase the size of programmable devices. For example, controllers used in power control and lighting devices have very few pins due to cost and size constraints.
Accordingly, there is a need in the art for improved techniques for configuring parameters of programmable devices that allow multiple parameters to be configured using fewer configuration terminals.